Wikipedia is great for uncontroversial, high-school stuff. The idea there is that it's generally a good, correct introduction to many subjects, so it acts a bit like a "dictionary" for us. In these cases, Wikipedia can be linked to, because its contents can be confirmed and refuted with a trivial Google search or by pulling out one's old high school textbooks. The choice of linking to Wikipedia is motivated by its clarity, not by its reliability.
On the other hand, linking to wikipedia for any claim can lead you to very strange places, and many of these overlap the typical questions we get on the site. So, it's not OK to use Wikipedia for anything which a lot of people believe, but it's incorrect. Clearly Wikipedia risks a confirmation bias there.
In other words:
OK to link to wikipedia when it's a well explained article on and there are very many other sources repeating the same content, making the point being sustained uncontroversial ("high school level").
NO to link to wikipedia when the point being made is non-trivial, e.g. when wikipedia is not properly referenced, or it's not a school level subject, or when the resources linked by wikipedia are weak.
This particular graph is probably correct, but clearly it's not enough. I wouldn't use it as evidence. Surely there's a paper upon which this (and the book) are based, and if not, then probably the data isn't very reliable...